Automated external defibrillator with shortened pause for rhythm analysis

Abstract

An automated external defibrillator (AED) is described that includes two electrocardiogram (ECG) analyzers. One of the ECG analyzers is only applicable to signal-noise-free ECG, and thus may be used during a "hand-off" analysis period in which no cardiopulmonary resuscitation (CPR) compression can be provided. The length of the "hand off" analysis period can be shortened by using the second ECG analyzer in conjunction with the first ECG analyzer. As a result, a greater proportion of CPR time is achieved throughout the course of cardiac arrest rescue.

Description

[0001] This application is a divisional application of patent application 201780022149.1, with an application date of March 30, 2017 and an invention title of "Automated External Defibrillator with Shortened Pauses for Rhythm Analysis". Technical Field

[0002] The present invention relates to an improved device and method for treating victims of cardiac arrest, and particularly to those patients in need of a treatment protocol that includes cardiopulmonary resuscitation (CPR) and defibrillation electrotherapy. Background Art

[0003] A defibrillator delivers a high-voltage pulse to the heart in order to restore normal rhythm and contractile function in a patient who is experiencing an arrhythmia, such as ventricular fibrillation ("VF") or ventricular tachycardia ("VT") without an accompanying spontaneous circulation. There are several classes of defibrillators, including manual defibrillators and automated external defibrillators ("AEDs"). An AED differs from a manual defibrillator in that the AED can automatically analyze an electrocardiogram ("ECG") rhythm to determine whether defibrillation is necessary. After determining that a shock is needed, the AED primes itself for delivering an electrotherapy shock, and then the AED advises the user to press a shock button to deliver the defibrillation shock. An AED that operates in this manner is referred to as semi-automatic. A fully automatic AED delivers a defibrillation shock without any user input. A fully automatic AED is commonly referred to as a fully automatic defibrillator in order to reduce confusion in terminology.

[0004] FIG. 1 is an illustration of a defibrillator 1 being applied by a user 2 to resuscitate a patient 4 suffering from cardiac arrest. The defibrillator 1 can be in the form of an AED or a fully automatic defibrillator that can be used by a first responder. The defibrillator 1 can also be in the form of a manual defibrillator for use by a paramedic or other highly trained medical personnel. Two electrodes 6 are applied by the user 2 on the chest of the patient 4 in order to acquire an ECG signal from the patient's heart. The defibrillator 1 then analyzes the ECG signal for signs of an arrhythmia using a shock analysis algorithm. The defibrillator only primes itself for delivering a high-voltage shock in the event that a shockable rhythm, such as VF or pulseless ventricular tachycardia (VT), is detected. The defibrillator 1 signals the user 2 via an audible or visual cue that a shock is recommended. The user 2 then presses a shock button on the defibrillator 1 to deliver the defibrillation shock.

[0005] It has been recognized that the faster a circulation can recover after the onset of VF (via CPR and defibrillation), the better the patient's chances of survival. For this reason, many AEDs (such as the one shown in FIG. 1) also include a user interface that includes audible, auditory, and visual cues for guiding the user through a programmed sequence of CPR and defibrillation shocks. The user interface may include detailed auditory cues for properly applying CPR compressions, an audible metronome for guiding the user to the proper compression rate, a visual display for showing the status and progress of the event, a signaler, a strobe light, etc. The sequence is pre-programmed into the device according to a protocol established by the local medical institution.

[0006] There are several ECG analysis algorithms that automatically analyze a patient's ECG to determine whether a defibrillation shock is appropriate for treating a potential cardiac rhythm. One such algorithm is generally described in U.S. Patent 6,671,547 to Lyster et al., entitled "Adaptive analysis method for an electrotherapy device and apparatus," and is incorporated herein by reference. The described algorithm relates to the patient analysis system (PAS) algorithm currently employed in AEDs such as the HeartstartTM FR3 AED manufactured by Royal Philips Limited of Andover, Massachusetts.

[0007] However, PAS and similar ECG algorithms for determining shockable conditions require a relatively noise-free ECG signal. PAS therefore requires that CPR be stopped during analysis because CPR causes artifacts in the ECG that mask VF when it is present or appear as VF when VF is not present. The former condition causes an undesired reduction in the sensitivity of the analysis, and the latter condition causes an undesired reduction in the specificity of the analysis. Thus, all existing protocols for CPR and defibrillation require at least a few seconds of periodic "hands-off" periods to allow the defibrillator to analyze the ECG with sufficient accuracy to be safe, useful, and effective for the patient.

[0008] Several problems arise from the need to interrupt CPR for ECG analysis. It has been shown that interruption of CPR compressions (even for only a few seconds) may reduce the likelihood of successful resuscitation. Thus, the requirement to stop CPR for ECG analysis before delivering a defibrillation shock may reduce the chances of a successful patient outcome. In summary, the hands-off time necessary for ECG analysis should be minimized to improve outcomes.

[0009] A number of prior art solutions have been developed for this problem, all of which relate to reducing the amount of delay between the cessation of CPR and the delivery of electrical therapy. One such solution, for example, is to develop an ECG analysis algorithm that can be used in the presence of CPR noise artifacts and can thus reduce or eliminate the need for a "hands-off" analysis period. One such ECG analysis technique involves wavelet transform analysis of an ECG data stream. Such a method is described by Addison in U.S. Patent No. 7,171,269, titled "Method of Analysis of Medical Signals," and is incorporated herein by reference. The '269 patent describes using wavelet transform analysis to decompose the signal into a cardiac signal and a CPR-related signal. Another example of such a method is employed by Coult et al. in International Patent Application No. PCT / US2012 / 045292, titled "Systems and Methods for Analyzing Electrocardiograms to Detect Ventricular Fibrillation." There, the electrocardiogram signal is interrogated by wavelets (such as Morlet, Myers, or Mexican hat wavelets) before being analyzed and classified as shockable ECG or non-shockable ECG.

[0010] Unfortunately, many of these ECG analysis techniques lack the accuracy necessary to reliably determine shockable rhythms in the presence of CPR noise artifacts, i.e., have insufficient sensitivity, while also being unable to avoid "false positive" shock decisions, i.e., have insufficient specificity. These techniques are also vulnerable to external electrical noise (such as line noise) and have not been adopted. Since accurate ECG analysis is important for proper patient management, there is a continuing requirement for periods of periodic quiet and artifact-free intervals, which of course also requires "hands-off" time.

[0011] The PAS algorithm is arranged to operate only on a noise-free ECG data stream. If the potential ECG rhythm is shockable, the PAS algorithm may require only a single five-second data buffer to make a shock decision. Thus, the time between the end of CPR and the delivery of a shock can be as short as five seconds.

[0012] However, if the underlying ECG rhythm is non-shockable, for reasons of algorithm specificity and sensitivity requirements, the PAS requires an additional five-second data buffer to arrive at a NSA decision of not recommending a shock. If the underlying ECG signal contains CPR compression noise or is contaminated by patient motion artifacts, the PAS may also require one or more additional ECG data buffers to make a decision that meets its required accuracy and specificity. Thus, for cases other than shockable ECG rhythms, the PAS requires at least 10 seconds of "hands-off" time to make such a determination.

[0013] What is needed is an improved method and apparatus for reducing the "hands-off" time required for ECG analysis. This need is particularly acute for situations where the underlying ECG rhythm is non-shockable or contaminated, despite a hands-off directive. Such improvements also increase the "hands-off" time for other types of ECG rhythms. Summary of the Invention

[0014] The inventors have recognized the limitations imposed by the prior art and have discovered techniques for eliminating the second and subsequent ECG data buffers (i.e., the extended analysis required by "hands-off" analysis such as PAS). In particular, the methods and apparatus of the present invention enable the use of a single ECG data buffer analysis during the "hands-off" period, where the single buffer analysis can be completed within five seconds. This can even be accomplished in cases where the underlying ECG rhythm is non-shockable or contaminated by artifacts.

[0015] In accordance with the principles of the present invention, a method for analyzing an ECG in a quiet situation is described. The method particularly relates to the "hands-off" interval between the end of a scheduled CPR compression period and the completion of a decision as to whether to be equipped for defibrillation shock or to recommend continued CPR. The method of the present invention employs techniques in which the ECG is analyzed by two different algorithms, each operating on data in a different frequency band. A first algorithm, similar to the aforementioned PAS, operates on a lower frequency data set in the ECG data buffer. A second algorithm, which will be described in more detail and is referred to as the Optimized Arrhythmia Recognition Technique (ART) algorithm, uses the generally higher frequency data set in the ECG data buffer. These algorithms operate simultaneously and independently. The selection criteria of the invention then achieve a faster decision during quiet periods with a decision accuracy similar to that of prior art methods.

[0016] In accordance with the principles of the present invention, an automated external defibrillator (AED) 810 for use during cardiopulmonary resuscitation (CPR) includes: an input section 812 for ECG signals; a user interface 818 having at least one of an audible instruction output and a visual display; a first ECG analyzer 831 in communication with the input section and operative to determine a shockable cardiac rhythm during a hands-off period characterized by the absence of CPR-related signal noise artifacts from the input section; and a second ECG analyzer 832 in communication with the input section and operative to determine a shockable cardiac rhythm in the presence of CPR-related signal noise artifacts from the input section. A processor 834 is in communication with the user interface, the first ECG analyzer, and the second ECG analyzer. The processor is operative to run software instructions to reduce the duration of the hands-off period only if both the first ECG analyzer and the second ECG analyzer determine the absence of a shockable cardiac rhythm. The processor is further operative to run software instructions to issue a user prompt to end the hands-off period and to restart CPR at the end of the reduced-duration hands-off period.

[0017] In other embodiments of the device, a second-order ECG buffer can be used by the first ECG analyzer to determine a shockable cardiac rhythm. Alternatively, a determination of the absence of a shockable cardiac rhythm can be made based on the single ECG buffer. The hands-off period can thus be reduced from ten seconds to a duration of approximately five seconds in some situations.

[0018] In an alternative embodiment, the second ECG analyzer can additionally act on an ECG buffer that occurs during a CPR compression period just prior to the hands-off period. The AED can then determine the absence of a shockable cardiac rhythm based on an analysis of the ECG buffer prior to the hands-off period and an analysis on a single ECG buffer that occurs during the hands-off period.

[0019] In addition, according to the principles of the present invention, a method for controlling a defibrillator during the application of CPR includes the following steps: providing a defibrillator having a first ECG analyzer and a second ECG analyzer, the first ECG analyzer being operable to determine a shockable cardiac rhythm during a hands-off period characterized by the absence of CPR-related signal noise artifacts, the second ECG analyzer being operable to determine a shockable cardiac rhythm in the presence of CPR-related signal noise artifacts; receiving an ECG signal data stream from two or more external electrodes in electrical contact with the patient and communicating with the first ECG analyzer and the second ECG analyzer, the ECG signal data including cardiac signals; prompting one of an audible output instruction or a visual output instruction for providing a continuous CPR period and a hands-off period, wherein the ECG signals are characterized by corruption from CPR compression noise artifacts during the CPR period and the absence of CPR compression noise artifacts during the hands-off period. The method continues with the following steps: analyzing the cardiac signals using the first ECG analyzer during the hands-off period and analyzing the cardiac signals using the second ECG analyzer. The method continues with the following steps: reducing the duration of the hands-off period to a reduced-duration hands-off period only if both the first ECG analyzer and the second ECG analyzer determine the absence of a shockable cardiac rhythm, and then issuing an audible output instruction or a visual output instruction for ending the hands-off period and / or for restarting CPR at the end of the reduced-duration hands-off period.

[0020] In another embodiment, the method may include a hands-off period that includes two or more data buffers, each of the two or more data buffers having a predetermined length, and wherein the reduced-duration hands-off period is one of the ECG data buffers in the duration. The hands-off period may be approximately ten (10) seconds in length, and the reduced-duration hands-off period may be approximately five (5) seconds in length.

[0021] In an alternative embodiment of the method, the second ECG analyzer may additionally act on an ECG buffer that occurs during a CPR compression period just prior to the hands-off period. The method may then determine the absence of a shockable cardiac rhythm based on an analysis of the ECG buffer prior to the hands-off period and an analysis on a single ECG buffer that occurs during the hands-off period.

[0022] As used herein for the purposes of this disclosure, the term "controller" is generally used to describe various devices related to the operation of a medical device, system, or method. A processor can be implemented in many ways (e.g., such as using dedicated hardware) to perform the various functions discussed herein. A processor is also an example of a controller that employs one or more microprocessors that can be programmed with software (e.g., microcode) to perform the various functions discussed herein. A controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware that performs some functions and a processor (e.g., one or more programmable microprocessors and associated circuitry) that performs other functions. Examples of controller components that can be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0023] In various embodiments, a processor or controller can be associated with one or more computer storage media (commonly referred to herein as "memory", such as volatile and non-volatile computer memory (such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tapes, etc.)). In some embodiments, the storage media can be encoded with one or more programs that, when run on one or more processors and / or controllers, perform at least some of the functions discussed herein. The various storage media can be fixed within the processor or controller or can be transportable, such that one or more programs stored thereon can be loaded into the processor or controller to implement aspects of the invention discussed herein. The term "program" or "computer program" is used herein in a general sense to refer to any type of computer code (e.g., software or microcode) that can be used to program one or more processors or controllers.

[0024] In various embodiments, the terms "low power standby circuit", "clock", "state change monitor", "comparator" apply to components that are generally known in the art and can be embodied in conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs) or can be integrated into the processor or controller described above. "Output" and "signal" can be understood to represent electrical or light energy pulses that represent a particular detection or processing result. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 illustrates a defibrillator according to the prior art and its use during cardiac rescue.

[0026] Figure 2a A process flow embodiment of an algorithm of the present invention for analyzing an ECG in the presence of noise artifacts from CPR compressions is illustrated.

[0027] Figure 2b Illustrates a process flow for determining a shockable cardiac rhythm based on an analyzed ECG according to an embodiment of the present invention.

[0028] Figure 3 Illustrates the frequency ranges of the ECGs predominantly used according to a first ECG analysis algorithm and a second ECG analysis algorithm of the present invention.

[0029] Figure 4 Illustrates, according to an embodiment of the present invention, from Figure 3 One of the filters of the second ECG analysis algorithm shown in the exemplary ECG output buffer.

[0030] Figure 5 Illustrates an exemplary two-dimensional decision surface for classifying an ECG signal as VF or undecided in a second ECG analysis algorithm according to an embodiment of the present invention.

[0031] Figure 6 Illustrates a flowchart method according to an embodiment of the present invention.

[0032] Figure 7 Illustrates a timeline of automatic decisions made by a defibrillator during operation according to an embodiment of the present invention.

[0033] Figure 8 Illustrates a functional block diagram of an external defibrillator according to the present invention.

[0034] Figure 9 Illustrates a user interface on an external surface of an AED according to an embodiment of the present invention.

[0035] Figure 10 Illustrates an exemplary user interface according to an embodiment of the present invention. Detailed Description

[0036] The shock recommendation algorithm that can be employed by the present invention is referred to as the Optimized Arrhythmia Recognition Technique (ART). This algorithm generally applies the principles of the aforementioned wavelet transform analysis to an ECG signal stream, but instead utilizes a series of fixed frequency bandpass filters in place of the wavelet transform. The set of bandpass filters is preferably constructed to have a frequency window with a shape similar to the Gaussian window used to generate a traditional Morlet wavelet. The following description refers to the use of the ART algorithm to suppress noise related to CPR artifacts. However, the inventors have noted that the ART algorithm can also be used without modification during quiet periods of the analysis where the hands are off. Such use of the ART during quiet periods where no CRP artifact related noise is present is actually guided by the methods and apparatus of the present invention.

[0037] The ART algorithm suppresses CPR artifact-related noise by selectively passing the relatively high-frequency components of a potentially corrupted ECG signal. ART is based on the following recognition by the inventors: While CPR and organized cardiac rhythms can occur at a similar repetition rate of approximately 1 to 2 Hz, typical CPR noise has relatively few high-frequency components in its signal (i.e., the signal tends to be a rounded waveform). Due to the rapid polarization and depolarization of the heart during a single cycle, cardiac activity tends to have a relatively large amount of high-frequency components. It is these high-frequency components that will be captured and analyzed by ART.

[0038] Turning now to the illustration, Figure 2a An exemplary process flow of the ART algorithm 200 of the present invention for analyzing an ECG in the presence of noise artifacts from CPR compressions is illustrated. At step 202, the method first preferably receives an ECG signal from two or more electrodes arranged in electrical contact with the patient's skin. The ECG signal is a time-varying voltage whose source is the patient's heart and possibly a voltage induced by CPR compressions being applied to the patient. The signal may also include other artifact signals external to the patient (such as patient thrashing and movement, external electrical noise, etc.). The ECG signal is preferably digitized into a signal data stream.

[0039] At the filtering step 206, the digitized ECG signal stream is processed by the ART filtering algorithm. Here, each data point in the signal stream is filtered through a set of first to fourth parallel filtering steps 206', 206'', 206''' and 206'''', through a set of first to fourth parallel filters, each filter having different bandpass characteristics. Each filter is preferably a finite impulse response filter. The number of filters and the bandpass characteristics of each filter can vary slightly within the scope of the present invention.

[0040] A preferred arrangement of the ART filter 306 is as follows and is shown in Figure 3 Four basic filters can be employed, which are generally applicable to Figure 2a the corresponding filtering step 206 in Figure 3As can be seen in the illustrative and exemplary embodiments, FLATS306’ has a center frequency of approximately 35 Hz, and CLAS1 306” has a center frequency of approximately 25 Hz. CLAS5 306”” is arranged to exclude radio frequency (RF) noise. And CLAS4 306”’ can be arranged to be useful for excluding false positive indications of VF caused by certain artifacts such as those attributed to transportation, muscle contraction, radio frequency interference, etc. by lower frequency components. In a preferred arrangement, the digitized ECG signal input results in four filtered ECG signal stream outputs.

[0041] In Figure 3 is also illustrated a comparison of the main frequency range in the ECG signal used by ART 310 and the frequency range of the first ECG algorithm 320 (such as PAS). Since PAS is optimal for use with a band at twenty (20) Hertz, it can be readily seen that different ECG signal data sets from the same ECG signal or data buffer are used by each of the two analysis algorithms. This indicates that the decisions from the first ECG analyzer and the second ECG analyzer employing the first ECG analysis algorithm and the second ECG analysis algorithm are somewhat independent.

[0042] As can be seen from Figure 4 it, many oscillations exist in the filtered signal such that there are many zero samples and near-zero samples in the buffer. To remove these effects, an additional envelope filter can optionally be applied to the data to remove localized zeros and non-zeros. Figure 4 Illustrated is the effect on the oscillatory output 402 of the CLAS1 filter 306” and the optional envelope filtering step 405.

[0043] At the buffering step 304, each stream of the filtered ECG signal data is segmented into sequential time periods (i.e., buffer ECG1, ECG2…ECGi). One preferred arrangement is non-overlapping adjacent buffers of 3.5 seconds in length. One sampling rate is 250 samples per second, which equals 875 ECG samples per buffer. The time period length and sampling rate are predetermined and can vary within the scope of the present invention. Each of the time points from each buffer has a value that depends on the input and the potential filter. In Figure 4 is shown an example of the filtered ECG buffer data set for CLAS1.

[0044] It is preferred and advantageous that the buffering step 204 occurs after the filtering step 206. By filtering before buffering, the method avoids filter transients at the edges of each buffer. Otherwise, the method would require longer overlapping buffers, which would require longer analysis times and attendant dragging effects on patient outcomes.

[0045] At step 208, the data in each of the filtered ECG buffers is compared with a threshold. The number of data points that fall within the threshold for that filtered ECG buffer (referred to as the score) is then calculated for use by analysis step 210. Of course, any mathematics equal to the number of data points (such as a ratio or fraction) can be substituted within the scope of this method step. For the purposes of this illustration, the score for the filtered ECG buffer for the FLATS filter is designated as the FLATS score. The score for the filtered ECG buffer for CLAS1 is designated as the CLAS score. Thus, Figure 2a It is illustrated that the threshold comparison step includes a threshold comparison for each of the parallel filtering steps, i.e., the first through fourth parallel threshold comparison steps 208', 208", 208"', and 208"".

[0046] The threshold for each of the filtered ECG buffer scores can be obtained in a number of ways, the determination of which falls within the scope of the present invention. The threshold can be fixed (e.g., predetermined), or it can be adaptive, e.g., calculated based on the average of all the data points in a particular buffer. For example, the FLATS buffer data set can be scored against a fixed threshold, and the CLAS buffer data set can be scored against an adaptive threshold.

[0047] Analysis step 210 begins by comparing the filtered ECG buffer scores with a predetermined decision surface. The decision surface constructed using a database of ECG signal data with CPR corruption noise defines which given sets of buffer scores indicate "VF" or "undecided" (i.e., other than VF). In Figure 5 An example of the decision surface in the CLAS and FLATS dimensions is illustrated. In this example, the decision surface 510 is constructed from corresponding pairs of one of the CLAS score and the FLATS score. Score pairs that fall within the decision surface 510 indicate a VF condition. Score pairs that fall outside the decision surface 510 indicate an undecided condition. Additional dimensions of the decision surface can be added using thresholds for additional filtered ECG buffers as desired to create a more accurate VF decision. Although only two dimensions are shown herein, three or more dimensions can also be used for decision surfaces that include other CLAS scores.

[0048] Analysis step 210 proceeds by comparing two or more buffer scores representing particular cardiac signal characteristics with the decision surface in order to determine VF or other than VF. For Figure 5 For the example shown in, an example CLAS / FLATS score pair is shown at 520, which indicates VF. Value pairs 530 that fall outside the decision surface 510 (e.g., above and / or to the right) indicate an undecided (i.e., other than VF) condition.

[0049] Each raw time segmented ECG buffer may thus be designated as either "shock advised" (i.e., corresponding to VF) or "no decision" (i.e., corresponding to "other than VF"). Once an ECG buffer is determined to be either shock advised or no decision, the ART repeats the steps of capturing, acquiring, filtering, and analyzing the next ECG buffer in the time sequence as shown in the "select next ECG buffer" step 212. The repeated process implements an additional method of combining each new buffer with the previous buffer to generate an overall continuous determination of the presence or absence of VF.

[0050] The methods described above have been shown to identify VF with accuracy sufficient to safely make a shock determination during the application of CPR and without the need for further confirmation of the analysis during the "hands off" time. The sensitivity of ART to VF for a single buffer of a CPR-contaminated ECG has been demonstrated to be over 70% (i.e., ART will detect true VF in over 70% of the events). Similarly, the specificity of ART has been demonstrated to be over 95% for a single buffer of the ECG (i.e., false positive VF indications will not be generated from over 95% of "other than VF" events).

[0051] It can also be noted that the performance of ART during "quiet" periods is close to that already demonstrated in existing PAS algorithms. The sensitivity of ART to VF on ECG data not contaminated by CPR artifacts is over 80%, compared to PAS on similar data at about 94%. The specificity of ART and PAS on a buffer of "clean" ECG to false VF is almost identical. Therefore, ART can also be used successfully and accurately during the hands-off analysis period.

[0052] Now go to Figure 2b , the method continues. A preferred embodiment of the method includes the aforementioned steps 202-212 performed in a processor (such as a DSP) separated from the steps mentioned in the following several paragraphs. Such an arrangement allows each ECG buffer to be analyzed and classified as VF or "no decision" in sequence relatively independently of the electric shock decision and control processor, which mainly only requires a classification data stream from the ECG signal stream. Another preferred embodiment of the method includes further separating the processing into multiple components. For example, the digitization of the ECG signal input at step 202 can be processed in a front-end chip (such as an ASIC), and the digital stream is fed into the DSP for filtering the digitized ECG signal stream into a separated filtered stream corresponding to method step 206. Yet another processor will then receive the filtered stream to perform the final classification, decision making and response processing functions described in the following paragraphs.

[0053] If VF is determined from the ECG buffer at analysis step 210 (i.e., the "advise shock" result), the underlying ECG rhythm is typically assumed to be a shockable cardiac rhythm. However, the optimal response to a VF determination may be more than just preparing the potential device to deliver electrotherapy. Instead, it may be preferred to obtain confirmation of the determination or otherwise communicate the determination to the user in a manner that does not overly interrupt ongoing cardiac rescue. A separate decision step 214 is thus provided for these purposes and is shown in Figure 2b as taking an input from analysis step 210. An example of such a scenario will be provided in the following paragraphs.

[0054] Since ART sequentially analyzes multiple ECG buffers during a CPR period that lasts several minutes, the cumulative sensitivity to the ongoing patient condition of VF will increase (i.e., more opportunities to detect a true VF condition). However, it should also be anticipated that the cumulative specificity will decrease (i.e., more opportunities to misinterpret a "non - decision" condition as VF). To maintain the specificity of the overall method at an acceptable level during this relatively long time period, an optional multi - buffer rule can be developed for making a shock decision from VF / non - decision decisions on temporally consecutive ECG data buffers. A repeated second analysis step 210 of the ECG buffer for a later second predetermined time period is provided to decision step 214. Decision step 214 then additionally bases its final decision on the second analysis step.

[0055] For example, analysis step 210 can determine that the cardiac rhythm is shockable as long as three temporally consecutive ECG buffers indicate VF. Otherwise, the analysis step indicates a non - shockable rhythm. It has been shown that under these rules, ART maintains a specificity of >95% during long CPR periods while the sensitivity remains >70%. In some cases, the sensitivity can exceed 95% and the specificity can exceed 98%. Such performance is acceptable for making shock decisions during the CPR period. In summary, given that decision step 214 essentially receives a stream of ongoing VF / non - decision ECG buffers, step 214 applies rules for the final decision on whether the potential device should be able to operably proceed with the delivery of a defibrillation shock.

[0056] The display step 215 can be initiated immediately after determining (such as a visual graphic or text message on a display, a light signal, or a subtle audible signal). Preferably, the display step 215 is provided even before the device is fully ready to deliver electrotherapy but in an unobtrusive manner that does not distract the user from continuing CPR compressions until the device is ready for shock delivery. On the other hand, there are some operating modes in which it may be preferable to not provide the user with any information about shock determination at all until the device is complete. Some lay users may not need to be distracted or frightened from providing CPR compressions by the mere indication that the device is preparing to deliver a shock.

[0057] In response to determining from decision step 214 that a shockable cardiac rhythm is present and electrotherapy should be provided, the arming step 216 begins. The arming step 216 can include charging a high-voltage charging circuit with sufficient energy to defibrillate the patient. The arming step 216 can include an audible and / or visual indicator that the arming step has begun, and some indication of progress towards being fully ready for shock delivery (step 217). For example, a dynamic bar graph indicator on a visual display can show the progressive filling of a bar graph corresponding to the increasing charge state of the high-voltage circuit. A text message on the display can also indicate that charging is in progress. The ECG display can be shown on the charging status display simultaneously with the progress indicator. Figure 7 An exemplary embodiment of such a display is illustrated. The audible progress indicator can include a continuous tone of increasing frequency that stops when the full charge state is reached.

[0058] Upon completion of the arming step 216, the electrotherapy device is fully ready to deliver a shock. After arming, it is preferable for a user prompt 219 to automatically occur to stop CPR to deliver the electrotherapy. An audible prompt from the speaker 830, illumination or a flashing shock button light 820, and / or a display indication 802 can be used to signal the user to stop CPR for shock delivery. See Figure 8 Examples of these indicators on the user interface 818. In the case of an AED, the prompt can also instruct the user to press the shock button 892 to deliver the shock. In the case of a fully automatic defibrillator, still at step 219, the shock can be automatically delivered immediately after the prompt occurs. If the user is using electrical insulating gloves or other such protective devices, any prompt to "stop CPR" at step 219 can optionally be omitted entirely.

[0059] In some cases, it may be desirable to delay the user prompt at step 219 to stop CPR until a minimum number of CPR compressions have been provided. For example, it may be desirable to perform at least 30 seconds of uninterrupted CPR before delivering the shock.

[0060] Immediately following the delivery of the electrotherapy, at step 222, the user can be automatically prompted to restart CPR. At step 220, the device can optionally be enabled to detect the delivery of the electrotherapy. Detection of the delivery can be obtained by sensing the output current, button presses, etc. The method then returns to the steps of capturing, obtaining, filtering, and analyzing according to the state of the cardiac rescue.

[0061] If at decision step 214 the ART reaches a non-shock determination (i.e., a "no" decision), the method proceeds directly to prompt step 222. As previously noted, the prompt should be issued as soon as possible in order to minimize the adverse "hands-off" time to the greatest extent possible.

[0062] The method steps described above allow CPR to continue until the moment of electrotherapy delivery and then immediately restart CPR thereafter. As a result, the proportion of "hands-on" time during cardiac rescue is increased, thereby improving the effectiveness of the overall treatment. The idle time waiting for the "hands-off" ECG analysis can be substantially eliminated, thus avoiding the loss of blood pressure and blood flow that occurs too quickly after the cessation of CPR. These benefits can be achieved along with the method's ability to handle the restoration of VF during the CPR period. If defibrillation occurs, the method simply detects VF and prepares for electrotherapy in the midst of ongoing CPR compressions.

[0063] Other advantages are provided by the method of the present invention. The inventors have found that using filters instead of wavelets somewhat reduces the computational load required for VF analysis and more effectively suppresses interference from power line noise or similar high-frequency noise. Most of these method steps can thus be accomplished in a single digital signal processor (DSP) that is arranged to receive an ECG signal stream, process the stream, and then output a continuous time-aligned and transformed ECG data stream. The DSP can also operate in parallel with a second processor that controls the final shock decision and delivery sequence in the AED. In addition, a series of filters can be easily adjusted to also provide more robust rejection of signals caused by DC offsets, 50 Hz and 60 Hz external power line noise.

[0064] Now turning to Figure 6 , a method for controlling a defibrillator during the application of CPR is described. The method particularly includes shock decisions made by both the ART ECG analysis algorithm and the known PAS ECG analysis algorithm described above. Preferably, these two algorithms operate simultaneously and during a quiet analysis period in the ECG signal that is free of any CPR-related signal noise artifacts.

[0065] The method starts at start step 602, where a decision has been made to use a defibrillator, for example, in a cardiac emergency or for a training process. A source or input section of an ECG signal is attached to the defibrillator (such as a set of patient electrodes connected to the defibrillator via wires).

[0066] At provision step 604, a defibrillator is provided that includes two different ECG analyzers. The first ECG analyzer includes an ECG analysis algorithm (such as the aforementioned PAS), which is specifically operable to automatically determine a shockable rhythm during a hands-off period characterized by a lack of signal noise artifacts in the ECG data stream. The output of the first ECG analyzer can be a "recommend shock" or "do not recommend shock" decision. If the first ECG analyzer detects confounding artifact noise, it can provide an output decision of "artifact".

[0067] Provision step 604 also provides a second ECG analyzer. The second ECG analyzer includes a second ECG analysis algorithm (such as the aforementioned ART), which is specifically operable to determine a shockable cardiac rhythm in the presence of CPR-related signal noise artifacts. The second ECG analyzer can of course also be used during a "quiet" period without artifacts. Since the second ECG analyzer must account for the uncertainty caused by artifacts, the sensitivity and specificity of its decisions may be slightly lower than those of the first ECG analyzer. Of course, both analyzers receive an input from the source of the ECG signal.

[0068] The method continues at reception step 606. Both the first ECG analyzer and the second ECG analyzer receive an ECG signal data stream from an input section that can be from a pair of electrodes in contact with the patient. Thus, the ECG signal data includes cardiac signals.

[0069] At the start of reception step 606, CPR compressions may or may not be in progress, depending on the state of the cardiac rescue at that time. Some AED rescue protocols indicate that CPR should be completed before the first defibrillation: some AED protocols indicate that defibrillation should be completed at the start of the rescue. Depending on the protocol, prompt step 608 causes the AED to issue audible and / or visual output instructions that can guide the user through successive periods of CPR and defibrillation. The defibrillation period is preferably before the hands-off period of the prompt, such that an artifact-free ECG data stream can be evaluated for a shockable rhythm.

[0070] It can be seen that an ART-like ECG analysis algorithm can optionally operate before any prompt step 608. At analysis step 607, the ART algorithm analyzes the ECG data stream even in the presence of CPR compression noise artifacts, so that ART is able to provide a shock decision for use even before the hands-off period.

[0071] Prompt step 608 issues an audible and / or visual prompt (such as instructions using "Stop CPR" and / or "Do not touch the patient") to start the hands-off period. Thus, the ECG signal then presumably begins to be characterized by the lack of CPR compression noise artifacts.

[0072] Shortly after prompt step 608, both the first ECG analyzer and the second ECG analyzer begin to analyze the cardiac signal at first analysis step 610 and second analysis step 612. The analysis is shown in Figure 7 starting at start time 702. The step 610 of analyzing the cardiac signal using the first ECG analyzer is preferably performed using an ECG analysis algorithm (such as PAS) optimized for use on artifact-free ECG signals. As can be seen in Figure 7 the first analysis is preferably performed on a sequence of ECG signal data buffers 714, 716 each having a length of approximately 5 seconds. Other time lengths are also contemplated, including overlapping of the buffers for a portion of the duration. Figure 7 It is also illustrated that the duration of the PAS analysis is typically two ECG data buffers 714 and 716, each having a predetermined length 707, which represents a total duration 712 of approximately ten (10) seconds in this example. If only the first analysis step is used, ten seconds is thus the minimum length of the hands-off period. As will be seen, this duration can be substantially shortened by the present invention.

[0073] Other ECG analysis algorithms (such as the "Solomon" ECG analysis algorithm used in the Philips MRX defibrillator manufactured in Andover, Massachusetts) can also be used in this step 610.

[0074] The first analyzer output step 614 issues a decision regarding each ECG data buffer. Thus, step 614 will sequentially issue a decision when the analysis of each data buffer is completed (e.g., approximately every five (5) seconds). This output step 614 preferably issues one of the following decisions, as shown in Figure 6 : "Advise shock" as indicated by an "Yes" output; "Do not advise shock" as indicated by a "No" output; and "Artifact". "Advise shock" indicates the presence of a shockable ECG rhythm with an acceptable statistical confidence. "Do not advise shock" indicates the lack of a shockable ECG rhythm with an acceptable statistical confidence. "Artifact" indicates that signal noise has been detected at a level too high to make a confident shock / no shock decision. The first analyzer output step 614 for each ECG buffer is provided to decision step 618.

[0075] See Figure 8, the second ECG analyzer 832 also operates on the ECG data stream at the start 702 of the hand-off period and at step 612 of analyzing the cardiac signal using the second ECG analyzer. The second ECG analysis algorithm (such as the aforementioned ART algorithm) can be optimized for different buffer lengths 706 (such as for 3.5 seconds as shown in Figure 7 . The ECG data buffer 704 of the second ECG analyzer is based on the same data stream as the data stream used by the first ECG analyzer, but can be optimized over different frequency ranges, see Figure 3 . The second analyzer output step 616 is preferably one of the following: "Suggest shock" as indicated by the "Yes" output from step 616; or "Undetermined" as indicated by the "No" output from step 616. The second analyzer output step 616 is provided to the decision step 618 at the end of each 3.5-second ECG data buffer.

[0076] Other ECG analysis algorithms can also be used in this step 612 (such as the "Vrhythm" ECG analysis algorithm used in the Philips FR2 defibrillator manufactured in Andover, Massachusetts, or other known ECG algorithms that take into account CPR compression noise artifacts in the ECG data stream).

[0077] The decision step 618 determines, based on the first ECG analyzer output and the second ECG analyzer output from steps 614 and 616, the condition in which the hand-off period can be shortened to a reduced-duration hand-off period. The determination made by the table is shown in step 618 and also in Table 1 below.

[0078] Table 1 – S (Suggest shock), NS (Not suggest shock, Undetermined), A (Artifact)

[0079]

[0080] As shown in these two tables, there can be several conditions in which the hand-off duration can be shortened. In particular, the condition where both the first ECG analyzer and the second ECG analyzer have determined in analysis steps 610, 614 and 612, 616 that a shockable cardiac rhythm does not exist can achieve a reduced-duration hand-off period. The reduced-duration hand-off period can thus include, for example, only one ECG data buffer that is approximately five (5) seconds in length. The method includes a reduction step 624 for this condition.

[0081] Also shown in decision step 618 and Table 1 are other conditions in which a hand-off period of reduced duration can be indicated. If both ECG analyzers determine "advisory shock" in their respective first ECG data buffers, then the duration can be reduced. If the first ECG analyzer is unable to make a decision due to artifacts, but the second ECG analyzer indicates an advisory shock, then the duration can be reduced. The method includes a second reduction step 628 for these conditions. Again, the preferred reduced duration is five (5) seconds long.

[0082] Other conditions at decision table 618 and Table 1 indicate that a reduction in the hand-off duration is not indicated or is not appropriate. In particular, if the ECG analyzers indicate conflicting decisions at steps 614 and 616 (i.e., one analyzer indicates "advisory shock" and the other analyzer indicates "no advisory shock"), then a secondary confirmation of the ECG analysis (e.g., another ECG buffer 716) is required. If "no advisory shock" from the second ECG analyzer is accompanied by an "artifact" indication from the first ECG analyzer, then a secondary confirmation of the ECG analysis (e.g., another ECG buffer 716) is also required. Decision table step 618 thus maintains the hand-off period at the initial duration at normal duration step 620. If artifacts from CPR are indicated, then an optional prompting step 622 can follow step 620 to remind the user to keep their hands off the patient. The method then returns to analysis steps 610, 612.

[0083] If the shock decision output at decision step 618 is indicated and the method 600 implements a hand-off period of reduced duration at step 628, then at arming step 630 the defibrillator immediately begins to arm its high voltage circuit for a defibrillation shock. Preferably, method 600 immediately begins an emitting step 632 as well as the arming step 630. The emitting step 632 includes audible and / or visual output instructions for ending the hand-off period and for guiding the user to deliver electrotherapy. If the defibrillator is fully automatic, then this emitting step 632 advises the user to keep their hands off the patient and that a shock is being delivered. After the emitting step 632 is complete, method 600 ends. The ending step can then proceed to another fixed CPR interval or return to step 606 for additional analysis.

[0084] The issuance step 626 follows the "no shock advised" decision from each ECG analyzer and the implementation of the reduced-duration hands-off period at step 624, and then the defibrillator processor implements the "restart CPR" issuance step 626. The issuance step 626 includes issuing instructions to end the hands-off period and to restart CPR at the end of the reduced-duration hands-off period, as well as one of an audible output or a visual output. Preferably, the issuance step 626 occurs immediately at the end of the reduced-duration hands-off period. The issuance step 626 should include a voice or visual cue indicating no shock advised and immediately starting CPR. One exemplary voice cue is "no shock advised, start CPR".

[0085] An alternative embodiment of the method uses the second ECG analyzer results obtained at optional step 607 (i.e., during the CPR compression period that occurs just prior to the hands-off period starting at step 608). The "shock / no shock" decision step from this step 607 can be provided to the decision step 618 in place of the outputs from steps 612, 616. The remaining steps of method 600 then occur as previously described.

[0086] Now describe the exemplary performance of the preferred embodiment. The ART and PAS ECG analyzers are applied to the cleanly annotated rhythms in the ECG development database. The PAS single buffer analysis requires 5 seconds of data and the ART single buffer analysis requires 3.5 seconds of data. Thus, the total length of the required data is 5 seconds. The following results are obtained.

[0087] Asystole - 96.8% (722 / 746) of the asystole cases require only one buffer for decision. The specificity (percentage of no shock advised) is 100%. The remaining 3.2% (24 / 746) of the asystole cases require a second buffer analysis.

[0088] Normal sinus rhythm (NSR) - 98.4% (438 / 445) of the NSR cases require only one buffer for decision. The specificity (percentage of no shock advised) is 100%. The remaining 1.6% (7 / 445) of the NSR cases require a second buffer analysis.

[0089] Organized rhythm and other non-asystole non-shockable rhythms (ORG) - 95.1% (1588 / 1670) of the ORG cases require only one buffer for decision. The specificity (percentage of no shock advised) is 100%. The remaining 4.9% (82 / 1670) of the ORG cases require a second buffer analysis.

[0090] All non-shockable situations (asystole, NSR, and ORG) - 96.1% (2748 / 2861) of non-shockable situations require only one buffer for decision-making. The specificity (percentage of cases where shock is not recommended) is 100%. The remaining 3.9% (113 / 2861) of non-shockable situations require a second buffer analysis.

[0091] Ventricular fibrillation (VF) - 87.1% (532 / 611) of VF cases require only one buffer for decision-making. The sensitivity (percentage of cases where shock is recommended) is 96.2% (512 / 532). The remaining 12.9% (79 / 611) of VF cases require a second buffer analysis.

[0092] Ventricular tachycardia (VT) - 70.4% (38 / 54) of VT cases require only one buffer for decision-making. The sensitivity (percentage of cases where shock is recommended) is 97.4% (37 / 38). The remaining 29.6% (16 / 54) of VT cases require a second buffer analysis.

[0093] All shockable situations (VF and VT) - 85.7% (570 / 665) of shockable situations require only one buffer for decision-making. The sensitivity (percentage of cases where shock is recommended) is 96.3% (549 / 570). The remaining 14.3% (95 / 665) of shockable situations require a second buffer analysis.

[0094] The exemplary method using these two algorithms for clean analysis returns results that meet the sensitivity and specificity constraints of the art. Currently, non-shockable rhythms require PAS for approximately 10 seconds or even longer for clean analysis. By using two algorithms, 96.1% of them require only 5 seconds of clean analysis with 100% specificity. Similarly, most shockable rhythms also require only 5 seconds of analysis with high sensitivity.

[0095] Now turning to Figure 8 , an apparatus incorporating the method of the present invention is described. The apparatus includes a medical device (such as an external defibrillator). Figure 8 A functional block diagram of an external defibrillator 810 according to an embodiment of the present invention is illustrated. The defibrillator 810 is configured to be an AED intended for use during cardiac rescue including CPR. It is designed to have a small physical size, lightweight, and relatively simple user interface that can be operated by a person without a high level of training or who would otherwise use the defibrillator 810 only infrequently. While this embodiment of the present invention is described in relation to its application in an AED, other embodiments include its application in different types of defibrillators (e.g., manual defibrillators, fully automatic defibrillators, and paramedic or clinical defibrillators / monitors).

[0096] The defibrillator 810 receives an input 812 of an ECG signal from, for example, two or more electrodes 816 that are connected to a patient. The ECG front-end circuit 814 is in electrical communication with the input 812 via a connector plug and socket or the like. The ECG front-end circuit 814 operates to amplify, buffer, filter, and optionally digitize the electrical ECG signal generated by the patient's heart to produce a stream of digitized ECG samples. The digitized ECG samples are provided to a controller 830, which may be a processor that combines a DSP and an ARM processor. One exemplary controller is a family of application processors manufactured by Texas Instruments Incorporated. In one embodiment of the device, the DSP performs all of the previously described filtering under the ART protocol and then passes multiple streams of the filtered ECG data to the ARM processor. The ARM buffers the stream of digitized ECG signal data into segments (buffers) corresponding to a predetermined time. The ARM performs result analysis on the filtered ECG data to detect VF, shockable VT, or other shockable rhythms. According to the present invention, the ARM uses the result analysis to determine the treatment plan that is most beneficial to the patient. These controller 830 portions of the DSP and the ARM thus operate together as a first ECG analyzer 831 and a second ECG analyzer 832, as described in method steps 602 to 632 above. Of course, the scope of the present invention is not limited to a particular DSP / ARM configuration. The foregoing and following functions may equivalently be implemented in a single processor or distributed among multiple processors, with the processor functions being controlled by the automatic execution of software instructions residing in a memory, such as memory 840.

[0097] The first ECG analyzer 831 is arranged to communicate with the input 812. The first ECG analyzer 831 is operable to determine a shockable cardiac rhythm during a hand-off period characterized by the absence of CPG-related signal noise artifacts from the input. An exemplary ECG analysis algorithm for this first ECG analyzer 831 is PAS, but other similarly arranged algorithms may be used.

[0098] The second ECG analyzer 832 includes an analysis algorithm that can determine a shockable rhythm in the presence of CPR-related signal noise artifacts. An exemplary second ECG analyzer 832 algorithm is the ART algorithm described previously, or may alternatively include Vrhythm or other artifact-suppressing ECG algorithms. Preferably, the second algorithm has a sensitivity of greater than about 70% and a specificity of greater than about 95% for shockable cardiac rhythms in the presence of CPR compression-related artifacts. The accuracy of this ECG analyzer is sufficient to safely and effectively evaluate the cardiac state of the input signal in the presence of CPR compression noise. Like the first ECG analyzer 832, the second ECG analyzer 832 communicates with the input.

[0099] Defibrillator 810 also includes a processor 834 that communicates with both the user interface 818 and the first ECG analyzer 831 and the second ECG analyzer 832. The processor 834 runs software instructions that control the defibrillator to operate generally in accordance with the Figure 6 previously described method. The processor 834 is specifically operable to run software instructions (such as those stored in 840) to control the duration of the hands-off period and reduce the hands-off period when indicated by the analyzers 831, 832. For example, the processor 834 runs software instructions to reduce the duration of the hands-off period only when both the first ECG analyzer 831 and the second ECG analyzer 832 determine that a shockable heart rhythm is absent. The processor 834 is also operable to run software instructions to issue a user prompt to end the hands-off period and restart CPR at the end of the reduced-duration hands-off period.

[0100] As previously described in method 600, the duration of the hands-off period can include an initial duration corresponding to two or more sequential ECG buffers. In this embodiment, the first ECG analyzer is operable to determine a shockable heart rhythm on each of the ECG buffers. The reduced-duration hands-off period can be the duration of a single ECG buffer used by the first ECG analysis algorithm. In this embodiment, the determination of the absence of a shockable heart rhythm from the first ECG analyzer is made based on a single ECG buffer. Thus, the user prompt to restart CPR can be issued faster, which results in a reduced overall hands-off time. In a case where the hands-off period is approximately 10 seconds and the reduced-duration hands-off period is approximately 5 seconds (i.e., the two-ECG buffer analysis is shortened to a one-ECG buffer analysis), the CPR prompt can be issued, for example, five seconds earlier. The user prompt in this embodiment can include one of a visual prompt and an audible prompt of "Shock not advised, start CPR".

[0101] Defibrillator 810 can alternatively be arranged according to an alternative operating method, where the processor 834 uses a determination from the second ECG analyzer 832 obtained from the CPR compression period that occurred just before the start of the hands-off period. In this alternative arrangement, the second ECG analyzer 832 determines that a shockable heart rhythm is absent during CPR, and then shortly after and during the hands-off period, the first ECG analyzer 831 determines that a shockable heart rhythm is absent in its first ECG data buffer. The two determinations cause the processor 834 to implement a reduced-duration hands-off period that ends at the end of the first ECG data buffer (e.g., at Figure 7 time 707 of

[0102] In addition, as previously described in the method of the present invention, if one or both of the ECG analyzers 831, 832 determine that a shockable rhythm is present and the processor 834 determines that a defibrillation shock is indicated, then the processor 834 also sends a signal to the HV (high voltage) charging circuit 860 to charge the HV energy storage source 870 in preparation for delivering a shock. When the HV energy storage source 570 is fully charged, the processor 834 directs Figure 9 either the shock button 892 or 992 on the user interface 918 of Figure 9 to start flashing via the illumination light 920 to redirect the user's attention from the task of providing CPR compressions to the task of delivering electrotherapy.

[0103] The defibrillator 810 can also convey audible information via the buzzer 824. The buzzer 824 can be activated, for example, by the device system monitor controller or the processor 834 when the HV charger has fully equipped the device for delivering a shock or to assist in warning the user to start or stop CPR compressions. The buzzer 824 can assist these functions through the concurrent activation of the LED 826 for these conditions.

[0104] Figure 9 An exemplary structural embodiment of the defibrillator 900 is illustrated and particularly generally corresponds to Figure 8 the defibrillator user interface 918 on the outer surface of the AED 800 that corresponds to the user interface 818 of the functional block diagram. The user interface 918 can include a visual display 902 that provides graphical and text information related to the status of the cardiac rescue. The user interface 918 can also include a speaker 930 that emits audible and sound cues. The LED 940 can provide a light-based signal for readiness or a fault. The structure of the LED 940 corresponds to Figure 8 the LED 826 of Figure 8 . The user interface 918 can also include first, second, and third configurable buttons 954, 956, 958 whose functions change depending on the status of the rescue or the configuration of the device. The configurable button functions can also be indicated by context labels 904, 906, 908 displayed on the visual display 902. For example, if the device is configured for an advanced operation mode, the display 902 can indicate that the adjacent configurable button 954 is configured as an "analyze" button 894. The analyze button 894 can be operated to truncate an ongoing rescue protocol. The truncation immediately stops the CPR session and readies the defibrillator for immediate electrotherapy delivery.

[0105] Go to Figure 10, shows an exemplary user interface of a portion of the method of the present invention as run by the device. Just before the start of the analysis when the hand leaves, the user interface 918 can warn the user to stop touching the patient (e.g., "Stop CPR", "Don't touch the patient", etc.) by means of the visual display 902. The display 1010 is an example of the visual display 902 at this time point. The input ECG can be displayed to show whether there are artifacts on the ECG. The defibrillator 810 can also present corresponding text messages or instructions that it is analyzing or that CPR compressions are still being detected. Audible instructions and guidance can be emitted from the speaker 930, which also corresponds to the display 1010 instructions. The LED 940 or the buzzer 824 can also be used to draw attention to the display.

[0106] The visual display 1030 for restarting CPR or the illuminated shock button display 1020 is preferably placed on the user interface 918 at the end of the hand-off period or a hand-off period of reduced length. Which display 1030, 1020 and when the display is provided is controlled by the processor 834 according to the method of the present invention. If the hand-off period can be reduced, the appropriate displays 1030, 1020 are provided at the end of, for example, the first ECG analyzer first ECG buffer time. Otherwise, the appropriate displays 1030, 1020 are shown at the end of the hand-off period. The time reduction is indicated by the reference numeral 1040.

[0107] The visual display 1030 preferably indicates that CPR should start or restart. As shown in 1030, the instructions can be placed on the display, as well as the ECG trace and the status of the detected CPR compressions. Timer indications can also appear. The indication can be accompanied by an audible instruction of "Shock not recommended, start PCR" as well as a flash light and buzzer sound.

[0108] The illuminated shock button display 1020 preferably indicates that a shock should be delivered immediately by illuminating the shock button. The corresponding instruction of "Don't touch the patient, press the shock button now" can be placed on the visual display 1030 at that time. In addition, the LED light 826 and the buzzer 824 can be activated to guide the user.

[0109] Additional modifications to the devices, methods, and displays as described above are covered within the scope of the present invention. For example, various configurations of user interface displays and audible indicators that achieve the objectives of the present invention described fall within the scope of the claims.

Claims

1. An automated external defibrillator (AED) (10) for use during cardiopulmonary resuscitation (CPR), comprising: an input section (812) for ECG signals; a user interface (818, 918) having at least one of an audible instruction output and a visual display; a first ECG analyzer (831) in communication with the input section and operative to determine a shockable cardiac rhythm during a hands-off period characterized by the absence of CPR-related signal noise artifacts from the input section; a second ECG analyzer (832) in communication with the input section and operative to determine a shockable cardiac rhythm during a CPR compression period in the presence of CPR-related signal noise artifacts from the input section, wherein the ECG signals during the CPR compression period are first filtered and then segmented into buffers, and wherein the second ECG analyzer is operative to determine a shockable cardiac rhythm on each of the ECG buffers in the ECG buffer; a processor (834) in communication with the user interface, the first ECG analyzer, and the second ECG analyzer, the processor operative to run software instructions to: (1) determine a first duration as the hands-off period only if both the first ECG analyzer and the second ECG analyzer determine the absence of a shockable cardiac rhythm; and (2) determine a second duration as the hands-off period if the first ECG analyzer and the second ECG analyzer determine different results, wherein the first duration is less than the second duration, wherein the processor is further operative to run software instructions to issue a user prompt to end the hands-off period and restart CPR at the end of the first duration.

2. The AED according to claim 1, wherein, the hands-off period includes an initial duration corresponding to two or more sequential ECG buffers, and wherein the first ECG analyzer is operative to determine a shockable cardiac rhythm on each of the ECG buffers.

3. The AED according to claim 2, wherein, the first duration is a single ECG buffer, and further, wherein the determination of the absence of a shockable cardiac rhythm by the first ECG analyzer is made based on the single ECG buffer.

4. The AED according to claim 1, wherein, the second duration is about 10 seconds, and further, wherein the first duration is about 5 seconds.

5. The AED according to claim 1, wherein, the user prompt includes one of a visual prompt and an audible prompt of "Shock not advised, start CPR".

6. The AED according to claim 1, wherein, the second ECG analyzer determines the absence of a shockable cardiac rhythm during a CPR compression period that occurred just before the hands-off period.

7. The AED according to claim 1, wherein, The second ECG analyzer determines the absence of a shockable cardiac rhythm during the hand-off period.

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